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Detection of Inosine via Strand Sequencing

Life beyond Earth could utilize similar informational polymers such as nucleic acids (DNA, RNA). However, the ability to detect non-standard bases or polymers would reduce the risk of false positives during life detection missions.

To demonstrate the potential for detection of non-standard bases using nanopore single molecule sequencing, we used Poly(deoxyinosinic-deoxycytidylic) acid, denoted Poly(dI-dC), a synthetic DNA polymer composed of alternating deoxyinosine (I) and deoxycytosine (C) bases (…CICICICICI…). Here we provide proof of principle data that strand sequencing (Oxford Nanopore Technologies, MinION R9 flowcells) can detect the non-standard inosine (I) nucleoside. Inosine is formed when the nucleobase hypoxanthine is attached to a ribose sugar, and is astrobiologically relevant: of the extraterrestrial nucleobases identified on meteorites, hypoxanthine is second in abundance only to the standard base guanine (G). The figure presents a histogram of the normalized ionic current (left) and the time varying ionic current signal for 20 seconds (right) for: (a) Lambda DNA: data representing 64 A,T,C,G 3-mer possibilities; (b) Poly(dI-dC): data representing 2 I,C 3-mer possibilities (CIC, ICI).